From India
Shakuntala Devi
Known as the “human computer”, in 1980 at Imperial College London she multiplied two 13-digit numbers in her head in 28 seconds.
She also wrote popular books of puzzles and mental arithmetic.
Central News Agency (Taiwan), Public domain, via Wikimedia Commons
Where you’ll meet Devi here
AlgebraLogicCounting
They turn up beside problems and lessons on these topics.
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Fibonacci
His Liber Abaci (1202) helped bring Hindu–Arabic numerals to Europe.
Its rabbit puzzle gives 1, 1, 2, 3, 5, 8, …, numbers Indian scholars had already met while counting rhythms in poetry.
A statue in Pisa; no likeness from his lifetime survives. Taty2007, CC BY-SA 4.0, via Wikimedia Commons (resized)